1. Field of the Invention
The present invention relates to the use of feline leukemia virus (FeLV) antigens for inducing, in a cat, antibodies to FeLV.
2. Brief Description of the Background Art
Feline leukemia viruses (FeLV) are replication-competent type C retroviruses, which are epidemiologically associated with the horizontal transmission of leukemia, aplastic anemia, and acute immunosuppression (feline AIDS) in cats. The genome of FeLV consists of a 60-70S single-stranded RNA which consists of a gag gene encoding for viral core proteins, a pol gene coding for reverse transcriptase, and an env gene which encodes for the gp70 and p15E vital envelope proteins.
Isolates of FeLV may be divided into subgroups A, B, and C based upon their interference patterns (Sarma et al., Virology 44:352-358 (1971)). FeLV-A is found in all isolates, whereas FeLV-B occurs in about 40% of all isolates. FeLV-C is fairly rare and like FeLV-B is always found in combination with FeLV-A (Jarrett et al., International Journal of Cancer 21:334-337 (1978)). FeLV-C is found in only about 1% of all viremic cats and only in cats with anemia (Onions et al., Nature (London) 296:156-158 (1982)).
Numerous attempts to produce a vaccine against feline leukemia have been unsuccessful. These attempts include those containing virus killed by irradiation, hydroxylamine, or paraformaldehyde, and vaccines utilizing mitomycin D inactivated virus (U.S. Pat. Nos. Nos. 3,966,907, 4,034,081, and 4,086,134) or based on the use of whole live infected cells and inactivated infected cells.
More recently, interest has focused on the use of purified FeLV molecules (Osterhaus et al., Journal of immunology 135(1):591-596 (1985)) and on the use of a FOCMA (Feline Oncornavirus Associated Cell Membrane Antigen) preparation (U.S. Pat. Nos. 4,331,793 and 4,434,157). A vaccine utilizing a FOCMA preparation is commercially available (Norden Laboratories, Lincoln, Nebr.). However, a recent study of the efficacy of this vaccine casts serious doubt as to its ability to protect cats from FeLV disease (Pedersen et al., Feline Practice 15:7-20 (1985)). Thus, a considerable need exists for antigen preparations that can stimulate the cat immune system and induce antibodies to FeLV.